Study on the Improvement in Bearing Capacity and Deformability of Prestressed High Strength Concrete Pile

本文综述了预应力高强混凝土桩（PHC桩）在侧向荷载作用下的试验研究。本研究的目的是探讨防止桩的脆性破坏和提高桩的变形能力的加固方法。主要对符合日本工业标准的b型PHC桩进行了试验。桩外径30厘米。轴向荷载的大小是假设桩在坚固地层上支承，标准贯入试验数约为50。也就是说，35tf是持续载荷。0 tf和70 tf为临时加载。105 tf为桩的极限承载。假设桩头固定在基础上，周围土体较软，桩抗剪跨与外径比为3.0。对于现场普遍使用的b型PHC桩，为防止其脆性破坏，应增加螺旋箍的数量。然而，在105 tf的轴向力作用下，即使在桩侧加7倍于一般桩侧加箍的螺旋箍，也无法阻止其发生。因此，试件的加固方法为：空心部分填充混凝土，采用高压螺旋箍加固。螺旋箍的数量是一般桩的25倍左右。结果表明，105 tf的轴向力可以保持到构件转角位移达到1/20 rad以上。此外，为了解决纵向钢筋断裂和桩头切断带来的问题，提高桩的变形能力，还对桩头与基础的连接进行了试验。结果表明：增加螺旋箍的数量，剪断桩头并对桩进行纵向加固，在桩的空心部分填充混凝土，在填充混凝土中纵向布置变形钢筋，并将变形钢筋粘结在基础中，是提高轴向承载能力和变形能力的有效方法。分析了桩基连接处的应力传递机理。为横向荷载作用下桩基抗震设计提供了基础数据。少

This report is the summary of the experimental study about the Prestressed High Strength Concrete Pile (PHC Pile) subjected to lateral load. The objective of this study was to investigate the reinforcing method by which the brittle failure could be prevented and the deformability of the pile could be improved.The B-type PHC piles of the Japanese Industrial Standard were mainly tested. The outer diameter of the pile was 30 cm. The magnitude of axial load was determined assuming that the pile was supported on firm stratum where the Standard Penetration Test Number was about 50. That is, 35 tf was for sustained loading. 0 tf and 70 tf were for temporary loading. 105 tf corresponded to the limit bearing load of the pile. The shear span to outer diameter ratio of pile was 3.0 assuming that pile head was fixed in the footing and the surrounding soil was fairly soft.As for the B-type PHC pile generally used in site, the amount of spiral hoop should be increased in order to prevent the brittle … More failure. It could not be prevented, however, under 105 tf of axial force, even if the pile was laterally reinforced by seven times amount of spiral hoop as much as that of generally used pile. So the specimens were reinforced as follows: the hollow part was filled with concrete and they were reinforced by high tension spiral hoop. The amount of spiral hoop was about 25 times as much as that of generally used pile. As the results, it was confirmed that the axial force of 105 tf could be kept until the displacement reached above 1/20 rad. in rotation angle of member.Furthermore, the experiment was carried out concerning the connection between the pile head and footing, in order to solve the problems generated by the rupture of longitudinal reinforcement and the cut-off of the pile head and to improve the deformability. As the results, the following method was proved to be effective for improving the axial load carrying ability and deformability: the amount of spiral hoop was increased, the pile head was cut off including longitudinal reinforcement of pile, the hollow part of the pile was filled with concrete, the deformed bars were longitudinally arranged in the filled concrete and they were bonded in the footing.The stress transfer mechanism in the pile-footing connection was analyzed. As a result, the fundamental data concerning the aseismic design of pile foundation subjected to lateral load. Less